Robot controlled adhesive dispensing systems must be capable of responding to commands from a robot or other similar control equipment so as to accomplish flow of a controlled amount of adhesive at particular points in the path of travel of an automatically positioned dispensing nozzle for the adhesive. A dispensing system without precise control of the flow of a highly viscous adhesive at particular points in the travel of the adhesive dispensing nozzle (such as might be supplied by ball valve arrangement, for example) restricts the controlled adhesive dispenser to dispensing adhesive on a workpiece at only one speed. If the automatically controlled (positioned and activated) dispensing nozzle in such an arrangement changes its speed at some point in its travel over the workpiece, then the dispensed bead of adhesive is uneven. Consequently, with such arrangement, the maximum dispensing speed is limited to the minimum speed at which the automatically controlled nozzle can traverse corners and other similar quick changes in direction. This is true even though the automatically controlled nozzle is designed to travel faster in straight lines. Since the flow rate of the adhesive being dispensed is preset by a ball valve or other arrangement for the slowest speed (i.e. around corners) at which the automatically controlled dispensing nozzle travels, the end result of moving faster would be to reduce the size of the adhesive bead being dispensed which is unacceptable in assembly operations.
Two prior approaches have been suggested to solve this problem. The first uses a metered shot technique which employs a piston and cylinder arrangement and the second uses a variable orifice to adjust flow rate a particular points in the travel of an automatically controlled dispensing nozzle. Neither approach has been satisfactory. To overcome this problem, the present invention has been devised.